In unison with the rapid advance of current information technology, a variety of information processing systems have been developed and a variety of recording systems have been employed therein. Among these recording systems, the thermal recording system has been in wide-spread use because of its advantages of light weight, low noise during printing, and ease of maintenance.
The thermal recording systems include two types, a thermal melt transfer type using thermal transfer recording sheets in which a colorant layer is comprised of a thermally melting material and a pigment and a sublimation type using thermal transfer recording sheets in which a colorant layer is comprised of a sublimatable dye. The thermal melt transfer type is characterized by color development with low energy. In contrast, the sublimation type requires high energy, but is adapted to produce full color images since it is easy to reproduce middle tone by utilizing differential energy applied.
In either type of thermal recording system, an increased quantity of heat is applied from the thermal head to a thermal transfer recording sheet for color development. Especially in the sublimation type, substantial heat is applied to substrates such as polyester films which are softened leading to a sticking phenomenon and heat distortion. This often can cause image distortion especially where high density is required, resulting in a failure to produce quality images.
The recent trend is toward the use of thin substrates for the purposes of increasing printing speed and reducing transfer energy. This, in turn, requires improvements in the heat resistance, slippage and the like of thermal transfer recording sheets.
One effective approach for such improvements is to coat thermal transfer recording sheets with silicone compositions. In order for silicone compositions be cured under sufficient conditions to comply with the requirements of thermal transfer recording sheets, some modifications are necessary. To this end, the same assignee as the present invention previously proposed a coating composition predominantly comprising a siloxane/styrene/(meth)acrylate copolymer (Japanese Patent Application Kokai No. 210160/1988).
However, prior art silicone compositions require heat for curing. Where an extremely thin film of up to 10 .mu.m, for example, is used as the thermal transfer recording sheet substrate, the film can be distorted during heat curing of silicone coatings. In addition, the cured coatings are less satisfactory in solvent resistance and the like. There exists a need for a thermal transfer recording sheet of quality capable of forming clear images while eliminating the above-mentioned problems.